Dewaxing hydrocarbon oils



Patented Dec. 5, 1933 UNITED STATES PATENT OFFICE DEWAXIN G HYDROCARBONOILS N Drawing.

Application September 16, 1931 Serial No. 563,221

10 Claim.

This invention relates to an improved process for the removal of waxfrom oils and especially for the removal of hydrocarbon waxes fromhydrocarbon lubricating oils. More particularly it relates to a diluentfor use in the dewaxing process.

The object of the invention is to provide a more eflicient and moreeconomical means for removing wax from oil and for the production oflubricating oils having superior properties. Further objects will appearas the description of the invention proceeds.

It is well known in the art of dewaxing hydrocarbon lubricating oils todilute such oils with petroleum naphtha, to chill the solution thusproduced to low temperatures in order to precipitate the wax and toremove thewax thus precipitated by suitable means, for instance, byfilter pressing.

It is also known that superior results can be obtained by thesubstitution of certain special diluents for the petroleum naphtha whichhas been generally used. The most important requirement to be met in theselection of such a special diluent, is that the diluent have the lowestpossible solvent power for wax consistent with its retaining thelubricating oil in solution. Many other properties must also be presentin order to render such a diluent satisfactory. One of the mostimportant of these properties is that the diluent must be such as toproduce a lubricating oil having a very low pour point. The pour pointis the lowest temperature at which the oil will flow when it is chilledwithout disturbance. It may be determined in accordance with MethodD97-30 of the American Society for Testing Materials. One of the chiefdisadvantages of the use of petroleum naphtha is the fact that the pourpoint of the dewaxed oil is from 20 to 40 F. higher than the dewaxingtemperature.

The production of viscous hydrocarbon oils having pour points in theneighborhood of 0 F. from stocks containing certain types of paraffinwax is difiicult or impossible by the use of petroleum naphtha or anyordinary diluent, since the refrigeration necessary to produce oilshaving these low pour points is expensive and since the wax is generallyprecipitated in a form which renders its separation from the oil verydiificult and frequently impossible. This situation is aggravated by thefact that the low temperatures required cause the solution to becomevery viscous, thereby decreasing the rate of the filtration operation bywhich the wax is removed.

However, by the use of certain diluents, it is possible to separate outpractically all the hydrocarbon wax at a temperature of 5 to 15 F.

This eliminates the necessity of using lower temperatures with theirconcomitant high refrigeration costs and low filter rates. The pourpoint of the resultant oil when using such a diluent is only slightlyhigher than the temperature of the dewaxing operation.

A satisfactory diluent or diluent mixture must not only have theproperties of separating out substantially all the wax in order to givean oil having a pour point in the neighborhood of the dewaxingtemperature, but it must also separate out the wax in a form suitablefor the facilitation of its removal from the oil. Furthermore, thediluent should be inexpensive, should be relatively non-toxic andnon-corrosive, should have a sumciently high volatility to facilitateits removal from the products of the process and should have asufficiently low volatility to prevent excessive evaporation losses.Another essential property of a satisfactory diluent or diluent mixtureis that it must be capable of being cooled to suitable dewaxingtemperatures without precipitating the dissolved hydrocarbon oil andwithout the separation of any additional solid or liquid phases otherthan the wax which it is desired to precipitate.

My present invention is concerned with the use of methyl acetate as aconstituent of such diluent mixtures. I have found that methyl acetatehas properties which adapt it remarkably well for use in dewaxinghydrocarbon oils, either alone or in combination with other solvents.One particular advantage which I found in methyl acetate is its lowviscosity, as a result of which, filter slurries are obtained havinghigh rates of filtration. Another advantage is the relatively lowboiling point of methyl acetate which facilitates its removal from thedewaxed oil and from the filter cake. This entails an added advantage inthat the methyl acetate can be removed at low temperatures, therebyavoiding the discoloration of the oil which frequently results from theuse of higher temperatures. It has also been found that methyl acetatepossesses to an unusual degree the desirable property of crystallizingout the wax in a form which facilitates its removal by filtration. Thisis attributed to the particular crystalline structure which the waxassumes. Furthermore, methyl acetate and its mixtures have to a highdegree all of the other properties set out above as requisites of asatisfactory diluent.

Because of its relatively low solvent power for wax and oil, I prefer touse methyl acetate as a constituent of a diluent mixture rather than asa one-component diluent. In order to retain the hexane and butane.

hood of 10 F., it would be necessary when working with most oils, to usean excessive amount of methyl acetate for a given amount of oil. Thisdifficulty has been overcome inthe;

present invention by the use of methyl acetate in conjunction withanother component whichhas a relatively high solvent power for oil andwax.

For instance, methyl acetate may be' used in combination with coal-tarbenzol, isopropyl ether, or petroleum naphtha.

As an example of a process'using such a diluent mixture, 3. distilled(overhead) lubricating fraction of Mid-Continent crude having aviscosity 015-74 seconds Saybolt at 210 F. maybe diluted at ordinarytemperatures with two and a half times its own volume of a mixtureofequal parts of methyl acetate and benzol. Other ratios of methyl acetateto benzol and other ratios of diluent to wax-bearing oil may be useddepending on the character of the oilbeing dewaxed and the particularconditions under whichv it is desired to use the process. In' general,the amount of methyl acetate necessary in the mixture decreases as theoil being treatedbecomes solution may then be pumped through asuitable,

filter press and the resultant wax cake washed with additional diluentmixture. The oil solution which has been passed through the filter pressis then redistilled in suitable distillation equipment and the oil anddiluent separated by fractionation. These various steps of the processare well known to those skilled in the art of. petroleum refining andthey will therefore not.

be described in further detail.

Altho the invention has been particularly de-- scribed in conjunctionwith the removal of the precipitated wax by filter pressing, it is to beunderstood that the wax may sometimes be removed by other suitablemeans, such as settling or centrifuging, which are Well known in theart.

In addition to its use with benzol, methyl acetate may be used as aconstituent of other diluent mixtures for dewaxing hydrocarbon oils. Theother constituent or constituents should be substances having a greatersolvent power for oil than does methyl acetate and should be present insuch proportion that the solution will persist as a single phase down tothe desired clewaxing temperature. Naturally this proportion will varywith the nature of the substance employed. Isopropyl ether, toluene andother substances may be used as constituents of such mixtures. I mayalso employ mixtures of methyl acetate with low boiling petroleumhydrocarbons such as When butane is employed it is necessary to maintainthe latter solvent mixture under super-atmospheric pressure because ofits high volatility. Suitable diluent I claim;

comprising compositions may be determined as desired by .oilinsolutionin methyl acetate at the desired .dewaxing temperature, that is in theneighborexperimentation based on the disclosure of my invention. Indewaxing special oils, for instance, highly aromatic hydrocarbon oils itwould be possible to use methyl acetate alone.

Altho I have described my invention by showingits application tospecific examples, these are given" for the purpose of illustration onlyand are not intended to limit the scope of the invention whose breadthis-measured only by the limitations of the following claims.

L In the dewaxing of hydrocarbon oils, the

'step' which comprises diluting the wax-bearing oil with adiluent'comprising methyl acetate.

2. In the dewaxing of hydrocarbon oils, the step which comprisesdiluting the wax-bearing oil with 'a' diluent mixture comprising betweenapproximately 30% and approximately methyl acetate.

v3. In the dewaxing of. hydrocarbon oils, the step which comprisesdiluting the wax-bearing oilwith a large amount of a diluent comprisingmethyl acetate and a material having good solvent powers for the dewaxedhydrocarbon oils.

4. In a process for the removal of hydrocarbon waxes from hydrocarbonoil the step which comprises diluting the wax-bearing oil with a diluentcomprising methyl acetate and benzol.

5. In the dewaxing of, hydrocarbon-oils, the step which comprisesdiluting the wax-bearing oil with a diluent containing more than 30%methyl acetate. I r

6. A process for the removal of hydrocarbon wax from hydrocarbon oilwhich comprises diluting the wax-bearing oil with a large volume of adiluent mixture containing methyl acetate and a material having goodsolvent powers for the dewaxed hydrocarbon oils, chilling the solutionthus produced to a low temperature to precipitate hydrocarbon wax,separation of the hydrocarbon wax, and removal of the diluent from thedewaxed hydrocarbon oil.

7. A process for the removal of hydrocarbon wax from hydrocarbon oilwhich comprises diluting the wax-bearing oil with from one to fourtimes-its own volume of a diluent mixture containing about equalquantities of methyl acetate and henzol, cooling'the solution to atemperature of 5 to l5 F. to precipitate hydrocarbon wax, separating thehydrocarbon wax, and removing the diluent from the hydrocarbon oil. 1

- 8.'In a process of removing wax from hydrocarbon oils wherein the oilis refrigerated to a low temperature and the wax is crystallized andseparated by filtration, settling or centrifuging, the step whichcomprises diluting the oil with a diluent mixture comprising methylacetate before refrigeration and recovering the said methyl acetate fromthe oil and wax subsequent to their separation.

. 9. Ina process for the removal of hydrocarbon waxes from hydrocarbonoils, the step which comprises diluting the wax-bearing oil with adiluent comprising methyl acetate and isopropyl ether.

- 10; In a process for the removal of hydrocarbon 11 waxes fromhydrocarbon oils, the step which comprises diluting the wax-bearing oilwith a diluent methyl acetate and toluene.

FREDERICK W. SULLIVAN, JR.

